This invention relates to ventless tire molds of the type having multiple inserts mounted in a circular outer ring back. The inserts have abutting surfaces which provide micro gaps between the inserts for venting gases from the mold and at the same time produce smooth even tread surfaces after the curing cycle is completed without any visible bleeder vents.
In the past it has been proposed to provide inserts made from cutting a circumferentially complete tread ring such as that shown in U.S. Pat. No. 5,234,326. The rows of inserts were mounted in a section of the annular portion of the mold and held in place by retention plates. In another embodiment two rows of blocks were mounted in sections of the lower mold half and held in place by another retention ring. The assembly of these molds is dependent on fastening the retention rings to the mold which requires screws or other fasteners for clamping the retention rings against the mold. This is not desirable for tire molds where the mold is exposed to high temperatures, expansion and corrosive gases making it difficult to maintain the fasteners. Dirt and other molding byproducts may collect between the retention plates and the mold at the tire forming and vulcanizing surfaces which creates a contamination problem. Also special vents are required to take the gases away from the inserts.
The present invention is directed to a multiple insert tire mold in which the mold inserts are mounted in the outer ring back without requiring the addition of retention rings or other devices which may cause problems with mounting and contamination of the mold surface. Also with the present invention the groove which retains the inserts also carries the gases away from the inserts.
According to one aspect of the invention there is provided a tire mold comprising:
a cylindrical tread forming outer ring member, a plurality of tread forming insert members supported by the outer ring member characterized by:
the outer ring member having a radially inner surface for engagement with a radially outer surface of each of the insert members,
a circumferentially extending slot in the radially inner surface of the outer ring,
the outer ring member having an opening in communication with said slot for inserting said inert members
each of the insert members having a radially extending rib for sliding engagement in the slot,
the slot having a circumferentially extending indentation at a position spaced from the inner surface of the outer ring: and,
the rib having a corresponding circumferentially extending projection at a position spaced from the radially outer surface for retaining each of the insert members in the outer ring while permitting sliding of the insert members in the slot for assembly and disassembly of the tread forming outer ring.
In accordance with another aspect of the invention there is provided a method of assembling a cylindrical tread forming outer ring for a tire mold wherein the outer ring has at least two segments with abutting radially extending end surfaces and each of the segments having a radially inner surface and a circumferentially extending slot in the radially inner surfaces with an opening in the end surfaces to the slot characterized by the steps of sliding rib members of a plurality of tread forming insert members into the slot at the opening for each of the segments and then connecting the segments to form a complete tread forming outer ring.
In accordance with still another aspect of the invention there is provided an insert member for mounting in an outer ring of a mold to form part of a cylindrical tread forming ring having a tread forming surface characterized by a radially outer surface having a circumferentially extending rib for sliding engagement in a slot in the outer ring, the rib having a circumferentially extending projection at a position spaced from the outer surface for retaining the insert member in the slot.